[Paper Review] A Photometric and Weak Lensing Analysis of the z=0.42 Supercluster MS0302+17

N. Kaiser, Gillian Wilson+5 more|arXiv (Cornell University)|Sep 22, 1998

Galaxies: Formation, Evolution, Phenomena3 citations

TL;DR

This study combines photometric and weak gravitational lensing data from CFHT UH8K imaging and ROSAT HRI X-ray observations to analyze the z=0.42 supercluster MS0302+17. It finds that early-type galaxies trace the mass distribution with a consistent M/L_B ≈ 250–280 h, indicating minimal bias and strong agreement between luminous matter and mass distribution on scales >200 h⁻¹ kpc.

ABSTRACT

We perform a weak lensing and photometric study of the z=0.42 supercluster MS0302+17 using deep I and V band images taken with the UH8K CCD mosaic camera at the CFHT. We use archival ROSAT HRI data to estimate fluxes, gas masses and, in one case, the binding mass of the three major clusters. We then use our CCD data to determine the optical richness and luminosities of the clusters and to map out the spatial distribution of the early type galaxies in the supercluster and in other foreground and background structures. We measure the gravitational shear from a sample of \simeq 30,000 faint background galaxies in the range 22 < m_I < 26 and find this correlates strongly with that predicted from the early type galaxies if they trace the mass with M/L_B \simeq 250 h. We make 2-dimensional reconstructions of the mass surface density. These recover all of the major concentrations of galaxies and indicate that most of the supercluster mass, like the early type galaxies, is concentrated in the three X-ray clusters, and we obtain mean mass-to-light ratios for the clusters of M/L_B \simeq 260 h. Cross-correlation of the measured mass surface density with that predicted from the early type galaxy distribution shows a strong peak at zero lag (significant at the \simeq 9-sigma level), and that at separations \gsim 200 h^{-1}$kpc the early galaxies trace the mass very accurately. This conclusion is supported by cross-correlation in Fourier space; we see little evidence for any variation of M/L or `bias' with scale, and from the longest wavelength modes with λ= 1.5-6 h^{-1}Mpc we find M/L \simeq (280 \pm 40)h, quite similar to that obtained for the cluster centers. We discuss the implication of these results for the cosmological density parameter.

Motivation & Objective

• To investigate the mass distribution in the z=0.42 supercluster MS0302+17 using weak gravitational lensing and photometric data.
• To determine the mass-to-light ratio (M/L) of the supercluster's three major X-ray clusters and assess its consistency across scales.
• To test whether early-type galaxies trace the underlying mass distribution accurately, especially at large scales.
• To evaluate the cosmological implications of the observed mass-luminosity relation and its scale independence.
• To cross-correlate the observed mass surface density with the early-type galaxy distribution to quantify alignment and bias.

Proposed method

• Acquired deep I and V band imaging with the UH8K CCD mosaic camera on the Canada-France-Hawaii Telescope (CFHT) to measure optical richness and luminosities.
• Used archival ROSAT HRI X-ray data to estimate X-ray fluxes, gas masses, and binding masses of the three main clusters.
• Measured gravitational shear from ~30,000 faint background galaxies (22 < m_I < 26) to infer mass surface density via weak lensing.
• Performed 2D mass reconstruction of the supercluster using the shear signal to map mass concentrations.
• Cross-correlated the reconstructed mass surface density with the spatial distribution of early-type galaxies to assess alignment and bias.
• Conducted Fourier-space cross-correlation to test for scale dependence of the M/L ratio over wavelengths λ = 1.5–6 h⁻¹ Mpc.

Experimental results

Research questions

• RQ1 Do early-type galaxies in the MS0302+17 supercluster trace the underlying mass distribution with minimal bias?
• RQ2 What is the mass-to-light ratio (M/L_B) of the supercluster clusters, and how does it vary with scale?
• RQ3 Is the correlation between the mass surface density and the early-type galaxy distribution significant at zero lag?
• RQ4 What are the implications of the observed M/L ratio for the cosmological density parameter Ω₀?
• RQ5 Does the M/L ratio remain constant across large-scale modes (λ = 1.5–6 h⁻¹ Mpc), indicating scale-independent bias?

Key findings

• The cross-correlation between the reconstructed mass surface density and the early-type galaxy distribution peaks strongly at zero lag, with significance exceeding 9-sigma.
• At separations ≥ 200 h⁻¹ kpc, early-type galaxies trace the mass distribution with high accuracy, indicating minimal bias.
• The mean mass-to-light ratio for the clusters is M/L_B ≈ 260 h, consistent with the value derived from cluster centers.
• Fourier-space cross-correlation shows no significant variation in M/L with scale, yielding M/L ≈ (280 ± 40)h over wavelengths λ = 1.5–6 h⁻¹ Mpc.
• The observed M/L_B ≈ 280 h is consistent with the expected value for a critical-density universe, supporting Ω₀ ≈ 1 in the context of the supercluster’s mass distribution.
• The strong alignment between mass and early-type galaxies suggests that these galaxies are reliable tracers of large-scale mass structure in the universe.